A fingerprint is the pattern of protrusions (namely ridges) and depressions (valleys) arranged linearly on an epidermal layer of a finger. As fingerprint has the characteristics of lifelong invariance, uniqueness and portability, fingerprint has become a synonym for biometric recognition and is widely applied in the field of authentication and identification of identity information such as security facilities and attendance systems.
Fingerprint recognition mainly adopts capacitive sensing technology. The principle of fingerprint recognition is that: when a finger touches capacitive electrodes arranged in an array in a fingerprint recognition module, protruded ridges make direct contact with the capacitive electrodes, and depressed valleys are far away from the capacitive electrodes, so that different sensing capacitance can be produced; fingerprint information of a contact person will be obtained by converting sensing capacitance into 2D image data; and hence the subsequent fingerprint comparison operation can be executed.
The capacitive electrodes are mainly made from conductive materials such as indium tin oxide (ITO). As limited by the accuracy of a mask and an etching process in the patterning process, the capacitive electrodes cannot be further manufactured to be finer nanometer size, so that the accuracy and the sensitivity of the capacitive fingerprint recognition mode can be limited.